Various intravital sugar chains play an important role in a mechanism for sustaining activities and lives of living organisms. In order to specifically reveal the functions of such sugar chains, it is necessary to analyze the functions of the sugar chains based on a complex structure thereof. Functional analysis of the sugar chains is carried out by the following technique. The structure of a sugar chain is reproduced part by part by analyzing the function of oligosaccharide whose structure is elucidated, so as to clarify the relation between the structure of a whole sugar chain and its functions.
As the technique of the functional analysis of sugar chains, the surface plasmon resonance (hereinafter referenced to as SPR) method is known, for example. That is, the ligand conjugate containing the oligosaccharide which imitates a part of sugar chain is immobilized on the sensor chip surface. By using the sensor chip having oligosaccharide immobilized thereon, substance, such as protein, which specifically interacts with oligosaccharide are identified. This makes it possible to properly evaluate a biological activity based on the structure of oligosaccharide.
Meanwhile, a single oligosaccharic molecule is not active enough. Therefore, it is necessary to collect sugar chains of oligosaccharide onto the sensor chip when evaluating a biological activity of an oligosaccharide. In other words, the use of collected sugar chains of oligosaccharide for analysis of interaction with a protein allows for evaluation of biological activity of sugar chains of oligosaccharide.
In view of this, the inventors of the present invention have so far found a linker compound including molecules having therein (i) moiety capable of being immobilizable onto the surface of the sensor chip and (ii) moiety capable of taking in sugar chains of oligosaccharide. Also, the inventors have so far found a ligand conjugate which includes the linker compound having one or two units of sugar chains of oligosaccharide introduced thereinto. Then, the inventors found that the use of such a ligand conjugate makes it possible to collect and introduce sugar chains of oligosaccharide onto the sensor chip (for example, see Patent document 1, Non-patent document 1).
[Patent Document 1]
Japanese Unexamined Patent Publication No. 836969/2003 (Tokukai 2003-836969; published on Mar. 19, 2003)
[Non-Patent Document 1]
Tentative Lecture Proceedings II in the 79th Spring Meeting, Chemical Society of Japan, Mar. 15, 2001, p. 1042
The use of the ligand conjugates disclosed in Patent document 1 and Non-patent document 1 makes it possible to arrange sugar chains of an oligosaccharide two-dimensionally on a surface of a sensor chip. However, there is a technical problem left in that it is difficult to arrange the sugar chains with high reproducibility.
That is, in order to analyze a biological activity of sugar chains of an oligosaccharide by using sugar chains of oligosaccharide molecules collected onto a surface of a sensor chip as described above, it is necessary to observe with high reproducibility an interaction between the sugar chains of the oligosaccharide and a protein, with the sugar chains of the oligosaccharide collected uniformly. Especially, in order to observe a biological activity of sugar chains of an oligosaccharide, it is important to evaluate a biological activity of sugar chains of oligosaccharide with high reproducibility by collecting sugar chains of three or more units of oligosaccharide onto a surface of a sensor chip so as to arrange the sugar chains two-dimensionally on the sensor chip with high reproducibility.
In the ligand conjugate disclosed in Non-patent document 1, one ligand conjugate has sugar chains of one or two units of oligosaccharides. In other words, the ligand conjugate consists of one linker compound and sugar chains of one or two oligosaccharides bonded to the linker compound. Therefore, in order to observe a biological activity of sugar chains of an oligosaccharide, it is necessary to collect sugar chains of three or more units of oligosaccharides onto a surface of a sensor chip by increasing a concentration of a ligand conjugate to collect the sugar chains, which are a ligand, in arranging the ligand conjugate onto the surface of the sensor chip.
The use of such techniques for collection of sugar chains of oligosaccharides makes it difficult to obtain with high reproducibility an arrangement of oligosaccharides wherein an interval between sugar chains of oligosaccharides is controlled so as to be a predetermined interval. Therefore, the functional analysis of oligosaccharide by using the conventional ligand conjugate makes it impossible to observe biological activities of oligosaccharides with high reproducibility. This might make it difficult to reveal a structure of sugar and to evaluate biological activities of oligosaccharides.
The present invention was made to solve the above problems. It is an object of the present invention to provide a novel linker compound with which oligosaccharides can be two-dimensionally arranged with high reproducibility while an interval between their sugar chains on a surface of a sensor chip is controlled. The present invention also provides a novel ligand conjugate which includes the linker compound and a sugar molecule introduced into the linker compound, a ligand carrier, and a process for producing the same.